64 bit features in a 32 bit application?

Question

I have a 32 bit application which I plan to run on 64bit Windows 7.

At this stage I cannot convert the entire application to 64 bit due to dependencies to thirdparty functionality.

However, I would like to have access to the xmm9-xmm15 registers in my SSE optimizations and also use the additional registers which 64 bit cpus provides in general while executing my application.

Is this possible to achieve with some compiler flag?

Answer 1

It seems to me that the best way would be to divide your program in more than one executable. The EXE compiled as 64bit can communicate with another 32-bit EXE used the 32-bit thirdparty DLL which you need. You will have some overhead in the communication and will have to implement Starting/Stopping of depended process, but you will have clear program architecture.

If you develop native C++ application you can implement the second EXE for example as the COM++ out-of-process object (LocalServer or even LocalService). You can consider the way to implement the COM server in C# (see here). Sometimes that way could simplify the implementation and you can use the advantages of both .NET and native programming.

Answer 2

Yes, you can. See this example for how.

As Christopher pointed out, this technique will not always work, but for this express purpose, to jump into a few lines of handcrafted assembly and make use of more registers, then put the result somewhere and then jump back to 32 bit mode, it should work out just fine.